Effect of luminal or circulating nitrite on colonic ion movement in the rat

The disposition of intravenously or luminally administered nitrite across the colonic mucosa and its effect on ion movement into or from the colon was assessed in anesthetized Porton rats using the isolated colon instilled either with sodium chloride (120 mM) or sodium chloride (80 mM) with sodium butyrate (40 mM). Ionic changes in the colon after intravenous injection of 10 mumol NaNO2 were compared with those occurring after injection of 10 mumol NaCl. After intravenous administration of nitrite, both nitrite and nitrate appeared in the colonic instillate in a ratio of 1:1. Nitrite increased chloride absorption (110%) and bicarbonate production (20%) when 40 mM butyrate was included in the instillate. Net sodium absorption, measured in the whole colon, was unchanged. Intravenous nitrite had no effect on ionic movement in the absence of butyrate. When NaNO2 (100 microM) was included luminally with the sodium chloride-butyrate instillate, bicarbonate production rate increased (25%), but sodium and chloride absorption were unaffected. Nitrite concentration in the instillate decreased during the 40-min experimental period at a rate of 0.275 nmol X min-1 X cm-2, and nitrate appeared at a rate of 0.037 nmol X min-1 X cm-2. We conclude that nitrate stimulates bicarbonate production in the colon, probably by stimulating the oxidation of butyrate, the main source of CO2 generation by the colonic mucosa.